1. Field of the Invention
This invention relates to improved systems for control of exhaust emissions of gases containing sufficient fuel values to generate high combustion temperatures. In one specific aspect the present invention relates to catalytic systems for control of exhaust emissions from internal combustion engines. More specifically, this invention relates to emissions control devices for fuel-rich internal combustion engines with very high reaction effluent tempeatures.
2. Brief Description of the Prior Art
Exhaust emissions from small internal combustion engines, such as are used for lawn mowers and small generator sets, are a significant source of atmospheric pollution by hydrocarbons and carbon monoxide. Such engines typically operate fuel-rich and therefore are particularly dirty as compared to an automotive engine, even without a catalytic converter. Although automotive emissions are now controlled by use of catalytic converters, such conventional devices are not considered feasible for small engine use because of inherently large size, high cost and system complexity relating to the need for air addition and to the need to limit the temperature of exhaust gases and exposed converter surfaces to safe values. The high emission levels of typical small engines means that destruction of those emissions results in a greater evolution of heat with a consequent higher converter temperature than for typical automotive catalytic converters. Further, small engine systems typically are much more exposed to gasoline spills and to operator contact, creating a hazard even with temperatures comparable to those for automotive catalytic converters. Effective means of suitable size and simplicity are thus required not only for the conversion reactor itself and for the addition and mixing of the air needed for oxidation of the exhaust fuel values to carbon dioxide and water but also for limiting temperatures to safe levels.
The present invention meets these needs by providing a passive system for dilution cooling of the hot effluent gases from engine emission control conversion devices.